The Global Positioning System (GPS) is a satellite-based system of navigation satellites that is relied upon to provide accurate position, velocity, and time (PVT) information to GPS-enabled receivers, particularly for military aircraft and weapon systems applications. Civilian applications rely on GPS PVT information to be highly accurate for aircraft, auto, and marine navigation as well as for surveying and other PVT information applications. A GPS-enabled receiver (also commonly referred to as “user equipment”) can acquire and lock on to synchronized ranging signals (navigation signals) broadcast from the GPS satellites, determine ranging measurements to the satellites, and triangulate to solve for position, velocity, and time (PVT).
A common problem for GPS user equipment is reflected navigation signals that are broadcast from the GPS satellites and then reflected off of other objects, such as buildings, large metal structures, an isotropic reflector, and the like. These reflected navigation signals are commonly referred to as “multipath” signals because they are reflected before being received, rather than being received as direct navigation signals via a direct path from a satellite to the GPS user equipment. When a GPS-enabled receiver locks on to reflected navigation signals and uses the multipath signals to determine the ranging measurements, a navigation error is introduced into the GPS user equipment PVT solution which can significantly degrade navigation accuracy.
Unlike a conventionally-shaped building, an isotropic reflector may be partially or fully spherical and can reflect several or even all of the navigation signals broadcast from the GPS satellites. The reflected navigation signals from an isotropic reflector that are received by GPS user equipment at some distance from the reflector will be delayed by an equal amount of time relative to the corresponding direct path navigation signals phase incident at the reflector, where the time delay is equal to the distance between the reflector and the user equipment divided by the speed of light.
Techniques currently exist to mitigate the effects of GPS multipath (reflected navigation signals), such as improved GPS user equipment antenna designs and signal processing methods. However, traditional GPS multipath techniques simply try to eliminate multipath reflections and/or reduce the error associated with reflected navigation signals which are considered corrupt navigation signals to be eliminated.